#include<cstdio>#include<cstring>#include<cctype>#include<algorithm>using namespace std;#define rep(i,s,t) for(int i=s;i<=t;i++)#define dwn(i,s,t) for(int i=s;i>=t;i--)int read(){	int x=0;char c=getchar();	while(!isdigit(c)) c=getchar();	while(isdigit(c)) x=x*10+c-‘0‘,c=getchar();	return x;}const int nmax=1e4+5;short int dp[nmax][nmax];int a[nmax];void maxs(int &a,int b){	if(a<b) a=b;}int main(){	int n=read();	rep(i,1,n) a[i]=read();	sort(a+1,a+n+1);	int ans=0,j,k;	rep(i,2,n-1){		j=i-1,k=i+1;		while(j&&k<=n){			if(a[j]+a[k]>2*a[i]) --j;			else if(a[j]+a[k]<2*a[i]) ++k;			else{				if(!dp[j][i]) dp[j][i]=dp[i][k]=3;				else dp[j][i]=dp[i][k]=dp[j][i]+1;				maxs(ans,dp[i][k]);--j;++k;			}		}	}	printf("%d\n",ans);	return 0;}